Inductance DC-DC converters for boosting supply voltages are already public. A challenge with this type of DC-DC converters, however, is size reduction since the converter requires inductive elements, and it has long been difficult to implement the converter as a semiconductor circuit. For this reason, when supply voltage boosting is required in portable equipment such as mobile telephone terminals or in integrated circuits, the task is accomplished by charge pump circuits (see Patent Document 1 (JP-A Hei 10-285911 Gazette), for example) which are built with capacitors and switching elements.
In liquid crystal display devices incorporated in mobile telephone terminals for example, a charge pump circuit is utilized in order to generate voltages (to be applied to scanning signal lines for example) to drive the liquid crystal display devices. In cases where such a liquid crystal display device includes thin film transistors (hereinafter abbreviated as “TFT”) provided by MOS (Metal Oxide Semiconductor) transistors made of polycrystal silicon, as constituent elements in individual pixel circuits, the charge pump circuit is sometimes formed together with these pixel circuits on the same insulation substrate which is provided by e.g. a glass substrate (see Patent Document 2 (JP-A 2007-60732 Gazette) for example).    Patent Document 1: JP-A Hei 10-285911 Gazette    Patent Document 2: JP-A 2007-60732 Gazette